Speed sensor probe location in gas turbine engine

ABSTRACT

A method for a gas turbine engine includes affixing a speed sensor probe in the gas turbine engine. The sensor probe is operable to determine a rotational speed in the gas turbine engine. The gas turbine engine includes a first spool that is coupled at a first axial position to a compressor hub that is coupled to drive a first compressor. The first spool is coupled at a second, different axial position to a fan drive input shaft that is coupled to drive a fan drive gear system. The second turbine is coupled through a second spool to drive a second compressor. The speed sensor probe is affixed at a third axial position that is axially forward of the first axial position and axially aft of the second axial position.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 13/837,236 filed Mar. 13, 2015, which is a continuation in partof U.S. patent application Ser. No. 13/368,677 filed Feb. 8, 2012, whichclaims priority to U.S. Provisional Patent Application No. 61/593,177,filed Jan. 31, 2012.

BACKGROUND

This disclosure relates to gas turbine engines and, more particularly,to the location of a speed sensor probe in a gas turbine engine.

A typical turbofan engine includes a compressor section and a turbinesection that is coupled to drive the compressor section and a fan of theengine. In a two-spool engine design, a high pressure turbine is coupledthrough a high spool to drive a high pressure compressor and a lowpressure turbine is coupled through a low spool to drive a low pressurecompressor. Typically, a probe is mounted in the engine to determine thespeed of at least one of the spools. One challenge in determining thelocation of the probe in the engine includes packaging concerns withregard to the engine architecture. Another challenge is to mount thespeed sensor probe in a location that can detect or mitigate certainengine events can cause an over-speed condition.

SUMMARY

A method for a gas turbine engine according to an example of the presentdisclosure includes affixing a speed sensor probe in a gas turbineengine. The sensor probe is operable to determine a rotational speed inthe gas turbine engine. The gas turbine engine has a fan, a fan drivegear system coupled to drive the fan about an engine central axis, acompressor section that has a first compressor and a second compressor,and a turbine section that includes a first turbine and a secondturbine. The first turbine is coupled to drive a first spool. The firstspool is coupled at a first axial position to a compressor hub that iscoupled to drive the first compressor and the first spool is coupled ata second, different axial position to a fan drive input shaft that iscoupled to drive the fan drive gear system. The second turbine iscoupled through a second spool to drive the second compressor. The speedsensor probe is affixed at a third axial position that is axiallyforward of the first axial position and axially aft of the second axialposition.

A further embodiment of any of the foregoing embodiment includes, priorto affixing the speed sensor probe, removing a used speed sensor probefrom the gas turbine engine such that the affixed speed sensor probereplaces the used speed sensor probe.

In a further embodiment of any of the foregoing embodiments, the gasturbine engine is accessed for the removing and the affixing through oneor more cowl doors.

A further embodiment of any of the foregoing embodiment includeselectrically disconnecting the used speed sensor probe and electricallyconnecting the affixed speed sensor probe.

In a further embodiment of any of the foregoing embodiments, the gasturbine engine further includes a fan output shaft coupled to be rotatedby the fan drive gear system and coupled at a fourth axial position tothe fan. The fourth axial position is distinct from the first axialposition and the second axial position. The fourth axial position isforward of the second axial position the third axial position.

In a further embodiment of any of the foregoing embodiments, thecompressor section is axially aft of the fan drive gear system.

In a further embodiment of any of the foregoing embodiments, the firstcompressor is a three-stage compressor.

A further embodiment of any of the foregoing embodiment includes atleast one sensor target coupled to rotate with the first spool.

In a further embodiment of any of the foregoing embodiments, the fandrive gear system is an epicyclic gear system.

In a further embodiment of any of the foregoing embodiments, theepicyclic gear system has a gear reduction ratio greater than 2.3:1.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example gas turbine engine.

FIG. 2 schematically illustrates the gas turbine engine of FIG. 1.

FIG. 3 illustrates a portion of a gas turbine engine that includes aspeed sensor probe.

FIG. 4 illustrates selected portions of another example gas turbineengine with a different sensor probe location.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flowpath whilethe compressor section 24 drives air along a core flowpath forcompression and communication into the combustor section 26 thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans as the teachings may be applied to other types ofturbine engines including three-spool architectures.

The engine 20 generally includes a first spool 30 and a second spool 32mounted for rotation about an engine central axis A relative to anengine static structure 36 via several bearing systems 38. It should beunderstood that various bearing systems 38 at various locations mayalternatively or additionally be provided.

The first spool 30 generally includes a first shaft 40 thatinterconnects a fan 42, a first compressor 44 and a first turbine 46. Inthe example shown, the first compressor 44 has three stages. The firstshaft 40 is connected to the fan 42 through a gear assembly of a fandrive gear system 48 to drive the fan 42 at a lower speed than the firstspool 30. The second spool 32 includes a second shaft 50 thatinterconnects a second compressor 52 and second turbine 54. The firstspool 30 runs at a relatively lower pressure than the second spool 32.It is to be understood that “low pressure” and “high pressure” orvariations thereof as used herein are relative terms indicating that thehigh pressure is greater than the low pressure. An annular combustor 56is arranged between the second compressor 52 and the second turbine 54.The first shaft 40 and the second shaft 50 are concentric and rotate viabearing systems 38 about the engine central axis A which is collinearwith their longitudinal axes.

The core airflow is compressed by the first compressor 44 then thesecond compressor 52, mixed and burned with fuel in the annularcombustor 56, then expanded over the second turbine 54 and first turbine46. The first turbine 46 and the second turbine 54 rotationally drive,respectively, the first spool 30 and the second spool 32 in response tothe expansion.

In a further example, the engine 20 is a high-bypass geared aircraftengine that has a bypass ratio that is greater than about six (6), withan example embodiment being greater than ten (10), the gear assembly ofthe fan drive gear system 48 is an epicyclic gear train, such as aplanetary gear system or other gear system, with a gear reduction ratioof greater than about 2.3:1 and the first turbine 46 has a pressureratio that is greater than about 5. The first turbine 46 pressure ratiois pressure measured prior to inlet of first turbine 46 as related tothe pressure at the outlet of the first turbine 46 prior to an exhaustnozzle. In a further embodiment, the first turbine 46 has a maximumrotor diameter D1 (FIG. 2) and the fan 42 has a fan diameter D2 suchthat a ratio of D1/D2 is less than about 0.6. It should be understood,however, that the above parameters are only exemplary.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7°R)]^(0.5). The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

FIG. 2 schematically illustrates selected components of theabove-described gas turbine engine 20. As shown, the first spool 30 iscoupled at a first axial position A₁ to a compressor hub 44 a that iscoupled to drive the first compressor 44. The first spool 30 is alsocoupled at a second axial position A₂ to a fan drive gear system inputcoupling 48 a to drive the gear assembly of the fan drive gear system48. For example, the input coupling 48 a can be the mechanical fuselocation or spline location. The gas turbine engine 20 further includesa speed sensor probe 70 that is operable to determine a rotational speedof the first spool 30. The speed sensor probe 70 is located at an axialposition A₃ that is axially aft of the first axial position A₁ and thesecond axial position A₂, and the speed sensor probe 70 is fixed orstationary relative to the first spool 30. In this example, the axialposition A₃ is also forward of the second compressor 52 and annularcombustor 56 and axially aft of the first compressor 44. It is to beunderstood that relative positional terms, such as “forward,” “aft,”“upper,” “lower,” “above,” “below,” and the like are relative to thenormal operational attitude of the gas turbine engine 20 and should notbe considered otherwise limiting.

The location of the speed sensor probe at the axial position A₃ ensuresthat that gas turbine engine 20 will be protected from an over-speedcondition in the event that either of the first compressor 44 or the fandrive gear system 48 becomes decoupled from the first spool 30. Forexample, if the compressor hub 44 a or the fan drive gear system inputcoupling 48 a fail, there will be a reduction in driven mass that causesthe rotational speed of the first spool 30 to increase. If the speedincrease is too great, the first turbine 46 can be damaged or fail. Bylocating the speed sensor probe 70 at the axial position A₃ that isaxially aft of the first axial position A₁ and the second axial positionA₂, the actual over-speed condition of the first spool 30 can bedetected in an event that causes decoupling. In comparison, if a speedsensor probe was positioned forward of axial position A₂, the speedsensor probe would not be able to properly detect an over-speedcondition caused by the first spool 30 becoming decoupled at thecompressor hub 44 a or fan drive gear system input coupling 48 a becausethe speed sensor probe would be reading the rotational speed from adecoupled component. Thus, the reading would not reflect the actualspeed of the first spool 30.

In a further example, the speed sensor probe 70 is in communication witha controller 72, such as a full authority digital engine control. Thespeed sensor probe 70 generates a signal that is proportional to thedetected speed of the first spool 30 and sends the signal to thecontroller 72. In one example method, in response to detecting arotational speed that exceeds a predetermined threshold rotational speed(i.e., an over-speed condition), the controller 72 changes (e.g.,decreases) a fuel supply to the annular combustor 56. In a furtherexample, in response to the over-speed condition, the controller 72ceases the fuel supply to the combustor 56. By decreasing or ceasing thefuel supply to the combustor 56, less energy is provided to the firstturbine 46. As a result, the speed of the first turbine 46 and firstspool 30 decreases.

FIG. 3 illustrates selected portions of another example gas turbineengine 120 that has a similar engine architecture as the gas turbineengine 20 of FIGS. 1 and 2. In this example, the first spool 30 iscoupled at the first axial position A₁ to the compressor hub 44 a, whichis coupled to drive the first compressor 44. The first spool 30 is alsocoupled at the second axial position A₂ to the fan drive gear systeminput coupling 48 a, which is coupled to drive the fan drive gear system48. A fan output shaft 42 a is coupled to be rotated by the fan drivegear system 48 to drive the fan 42. A speed sensor probe 170 is locatedat the third axial position A₃ that is axially aft of the first axialposition A₁ and the second axial position A₂. The speed sensor probe 170is mounted to and accessible through an intermediate case 78.

At least one sensor target 170 a is coupled to rotate with the firstspool 30. In one example, the at least one sensor target 170 a includesa plurality of sensor targets 170 a. In an embodiment, the sensor target170 a includes slots or teeth such that rotation of the slots or teethcan be detected by a detector in the speed sensor probe 170. Thedetector can be a hall-effect sensor, a laser sensor, an optical sensoror the like that is capable of detecting the rotation of the slots orteeth. The speed sensor probe 170 generates a signal that isproportional to the detected speed and sends the signal to thecontroller 72.

In this example, the first spool 30 is coupled to the compressor hub 44a at a splined connection 80, which also defines the first axialposition A₁. The first spool 30 is supported by a bearing 82, which isfixed relative to front center body case 84 and positions the firstspool 30 relative to the engine central axis A. The fan drive gearsystem input coupling 48 a extends forward from the bearing 82 and iscoupled at its forward end to the fan drive gear system 48. Rotation ofthe first spool 30 drives the fan drive gear system input coupling 48 a,which drives the fan drive gear system 48.

As described above, decoupling of the first compressor 44 at thecompressor hub 44 a from the first spool 30 or decoupling of the fandrive gear system input coupling 48 a from the first spool 30 reducesthe driven mass of the first spool 30 and first turbine 46. Bypositioning the speed sensor probe 170 at axial position A₃ axially aftof axial position A₁ and axial position A₂, an over-speed condition canbe properly determined.

In this example, in a decoupling event at the compressor hub 44 a or thefan drive gear system input coupling 48 a, the bearing 82 maintains theposition of the first spool 30 with regard to the engine central axis A.Thus, the first spool 30 continues to rotate in the decoupling event. Incomparison, if the first spool 30 decouples at a position that isaxially aft of axial position A₁, the bearing 82 would not maintain theaxial alignment of the first spool 30. The first spool 30 would misalignsuch that rotating and static hardware would mesh to slow or stop therotation of the first spool 30 and first turbine 46. Thus, there is noneed to locate the speed center probe 170 farther axially aft of theaxial positions A₁ and A₂. Moreover, locating the speed sensor probe 170forward of axial positions A₁ and A₂ would not enable the speed sensorprobe 170 to properly detect the actual speed of the first spool 30should a decoupling event occur at the compressor hub 44 a or the fandrive gear system input coupling 48 a.

In a further example, the location of the speed sensor probe 70 at theaxial position A₃ also facilitates assembly of the gas turbine engine20/120, maintenance and the like. An example method of assembling thegas turbine engine 20/120 includes affixing the speed sensor probe70/170 at the axial position A₃ that is axially aft of the first axialposition A₁ and the second axial position A₂. For instance, the speedsensor probe 70/170 is periodically replaced in the gas turbine engine20/120 as regular maintenance or if the speed sensor probe 70/170becomes damaged. Thus, the used speed sensor probe 70/170 is removed anda new speed sensor probe 70/170 is affixed as a replacement.

In a further example, the speed sensor probe 70/170 is affixed at axialposition A₃ using fasteners, such as bolts. In a replacement operation,the used speed sensor probe 70/170 is removed by electricallydisconnecting the speed sensor probe 70/170 and removing the fasteners.Once removed, the new speed sensor probe 70/170 is installed intoposition, the fasteners are tightened and the new speed sensor probe70/170 is electrically connected. In one further example, the axialposition A₃ of the speed sensor probe 70/170 is accessible through oneor more cowl doors.

FIG. 4 illustrates selected portions of another example gas turbineengine 220 that has a similar engine architecture as the gas turbineengine 20 of FIGS. 1 and 2. In this example, sensor probe 270 is in adifferent axial location than the sensor probe 70/170. Similar to sensorprobes 70/170, the sensor probe 270 is axially aft of the second axialposition A₂. Unlike sensor probes 70/170, the sensor probe 270 isaxially forward of the first axial position A₁. As can be appreciated, asensor target, similar to sensor target 170 a can be coupled to rotatewith the first spool 30. The sensor probe 270 generates a signal that isproportional to the detected speed and sends the signal to thecontroller 72. Additionally, any of the sensors probes 70/170/270 can betiming sensors that generate one or more signals per revolution of thefirst spool 30 that can be used to determine speed.

The fan output shaft 42 a is coupled at a fourth axial position A₄ tothe fan 42. The fourth axial position A₄ is forward of the second axialposition A₂ and the third axial position A₃. As can also be appreciatedfrom the drawings, the compressor section 24 is axially aft of the fandrive gear system 48 and the axial positions are distinct from oneanother.

The location of the speed sensor probe at the axial position A₃ ensuresthat that gas turbine engine 20 will be protected from an over-speedcondition in the event that either of the first compressor 44 or the fandrive gear system 48 becomes decoupled from the first spool 30.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. A method for a gas turbine engine, the methodcomprising: affixing a speed sensor probe in a gas turbine engine, thesensor probe operable to determine a rotational speed in the gas turbineengine, the gas turbine engine includes a fan, a fan drive gear systemcoupled to drive the fan about an engine central axis, a compressorsection including a first compressor and a second compressor, and aturbine section that includes a first turbine and a second turbine, thefirst turbine coupled to drive a first spool, the first spool beingcoupled at a first axial position to a compressor hub that is coupled todrive the first compressor and the first spool being coupled at asecond, different axial position to a fan drive input shaft that iscoupled to drive the fan drive gear system, and the second turbinecoupled through a second spool to drive the second compressor, and thespeed sensor probe being affixed at a third axial position that isaxially forward of the first axial position and axially aft of thesecond axial position.
 2. The method as recited in claim 1, including,prior to affixing the speed sensor probe, removing a used speed sensorprobe from the gas turbine engine such that the affixed speed sensorprobe replaces the used speed sensor probe.
 3. The method as recited inclaim 2, wherein the gas turbine engine is accessed for the removing andthe affixing through one or more cowl doors.
 4. The method as recited inclaim 2, including electrically disconnecting the used speed sensorprobe and electrically connecting the affixed speed sensor probe.
 5. Themethod as recited in claim 1, wherein the gas turbine engine furthercomprises a fan output shaft coupled to be rotated by the fan drive gearsystem and coupled at a fourth axial position to the fan, the fourthaxial position being distinct from the first axial position and thesecond axial position, and wherein the fourth axial position is forwardof the second axial position the third axial position.
 6. The method asrecited in claim 1, wherein the compressor section is axially aft of thefan drive gear system.
 7. The method as recited in claim 1, wherein thefirst compressor is a three-stage compressor.
 8. The method as recitedin claim 1, including at least one sensor target coupled to rotate withthe first spool.
 9. The method as recited in claim 1, wherein the fandrive gear system is an epicyclic gear system.
 10. The method as recitedin claim 1, wherein the epicyclic gear system has a gear reduction ratiogreater than 2.3:1.